### PCB Design Guidelines: Line Width, Spacing, and Via Specifications

#### 1. Line Width and Spacing

– **Minimum Line Width**: 6 mils (0.153 mm)

When designing PCBs, the minimum line width should not be less than 6 mils (0.153 mm). Lines narrower than this are typically not manufacturable. For **multilayer boards**, the inner layer’s minimum line width and spacing are generally set at **8 mils**. However, if design conditions allow, it is advisable to increase the line width. Larger line widths improve manufacturability, reduce the risk of defects, and result in higher yield during production. A common industry design practice is to aim for **10 mils** as the ideal line width. This is an essential consideration during the design phase.

– **Minimum Line Spacing**: 6 mils (0.153 mm)

The minimum line spacing refers to the gap between two adjacent traces (line-to-line) and should also be **6 mils** (0.153 mm) or greater. Additionally, the spacing from a trace to a pad should not be less than **6 mils**. From a production standpoint, a larger spacing is preferred to ensure easier manufacturing. A typical design standard is **10 mils** for line spacing. Again, if the design allows, increasing the spacing is recommended to enhance production reliability.

– **Distance Between Trace and Outline**: 0.508 mm (20 mils)

The gap between the trace and the PCB outline should be a minimum of **20 mils** (0.508 mm). This spacing ensures the integrity of the trace during PCB fabrication and minimizes the risk of edge-related defects.

#### 2. Via Specifications (Conductive Holes)

– **Minimum Via Hole Diameter**: 0.3 mm (12 mils)

The diameter of the via hole should not be smaller than **0.3 mm** (12 mils). Smaller vias can cause problems during the manufacturing process and may lead to unreliable connections.

– **Pad Size for Vias**:

The pad size associated with a via should not be smaller than **6 mils** (0.153 mm) on one side, and it is often recommended to increase this size to **8 mils** (0.2 mm) for better reliability. While the pad size can be adjusted based on design requirements, ensuring a minimum of **6 mils** is crucial for reliable production and functionality.

### Key Takeaways:

1. **Larger Design Features = Better Manufacturability**: Both line width and spacing should be as large as possible within the constraints of your design. This increases production yield and reduces potential defects.

2. **Design with Manufacturability in Mind**: Common industry standards for line width and spacing (10 mils) are often ideal for PCB production, but increasing these values can further improve the success rate in manufacturing.

3. **Via Hole and Pad Considerations**: Ensure via hole sizes and pad dimensions are adequate to support reliable electrical connections.

Designing within these guidelines ensures that your PCB is manufacturable, reliable, and of high quality, reducing risks during the production process.


**PCB Design Guidelines: Key Considerations for Optimal Manufacturing**

**1. Via Hole Spacing**

The spacing between via holes (edge to edge) should not be less than 6 mils, with an ideal spacing of 8 mils or more. This requirement is crucial for reliable manufacturing and signal integrity. Close via hole spacing can make the PCB more difficult to manufacture and lead to potential issues in the final product.

**2. Pad and Outline Spacing**

The distance between the PCB pad and the outline line should be at least 0.508 mm (20 mils). This spacing ensures there’s enough room for routing and prevents potential issues during the fabrication process. Adequate clearance from the outline is essential for maintaining board integrity and reducing the risk of edge defects.

**3. Through-Hole (PTH) Pad Design**

Through-hole pads (also known as PTH) are critical for reliable component insertion and soldering. The pad size must always be larger than the component pin. A recommended minimum increase is 0.2 mm; for example, if the component pin diameter is 0.6 mm, the hole should be designed at least 0.8 mm in diameter. This clearance accounts for manufacturing tolerances and ensures smooth component insertion.

– The outer ring of the PTH pad should have a minimum width of 0.2 mm (8 mils). Larger values are preferable for stronger mechanical reliability and easier assembly.

– The spacing between through-holes (edge to edge) should not be less than 0.3 mm. Again, larger spacing is more beneficial for both manufacturing and performance.

**4. Anti-Soldering and SMD Window Requirements**

For areas near plug-in holes, a window for anti-soldering must be designed with a minimum of 0.1 mm (4 mils) on each side. This ensures sufficient clearance to prevent solder bridges and manufacturing errors, particularly in single-sided Surface-Mount Device (SMD) windows.

**5. Character Design**

The legibility of characters on the PCB is essential for both assembly and maintenance. The following specifications should be followed:

– The character width should not be less than 0.153 mm (6 mils).

– The character height should not be less than 0.811 mm (32 mils).

– The width-to-height ratio should ideally be 5:1. For example, a character width of 0.2 mm should have a height of 1 mm.

Poorly designed characters can lead to production difficulties and unclear labeling, which may affect assembly and troubleshooting processes.

**6. Non-Metalized Slot Hole Spacing**

For non-metalized slot holes, the minimum spacing should be no less than 1.6 mm. Insufficient spacing can lead to milling complications, increasing both production time and costs. Proper spacing ensures smoother processing and improves the overall quality of the final PCB.

**7. Panelization (Imposition) Guidelines**

Panelization refers to how multiple PCBs are arranged on a single manufacturing panel. There are two main types: no-gap and gap panelization.

– **No-Gap Panelization:** In this case, the board edges are placed directly adjacent to each other.

– **Gap Panelization:** A gap is left between boards for easier separation after manufacturing. The gap should be no less than 1.6 mm for a 1.6 mm thick board. Smaller gaps can cause difficulty in milling and increase the risk of damage during the separation process.

For gap panelization, the typical gap is around 0.5 mm, with a 5 mm process edge along the perimeter.

**8. V-Cutting Considerations**

– **V-Cut Length:** The length of the V-cut should be greater than 8 cm to avoid issues with the machine’s operation. V-cuts smaller than this may lead to the PCB falling into the machine during processing.

– **V-Cut Width:** The width of the V-cut must be less than 32 cm. If the board width exceeds this, it may not fit into the V-cutting machine, which is a limitation in many PCB manufacturing processes.

V-cuts can only be made in straight lines, so it’s important to consider the shape and layout of the board. If straight-line cuts aren’t feasible, you can increase the spacing between holes or use other techniques to bridge connections.

**Conclusion**

Following these PCB design guidelines is essential for ensuring that the board can be manufactured efficiently and meets both functional and quality standards. Clear and structured pad designs, proper spacing for holes, and attention to detail in features like characters and slot holes will ultimately help reduce manufacturing complexity and improve the overall quality of the PCB.